It is well known in the railway car art to provide a railway car which is convertible from a hopper car with bottom doors to a car with a flat bottom with foldable members which form the bottom. An example of such a car is found in U.S. Pat. No. 2,648,293.
In assembling railway freight cars, it is expensive to provide a line, or a series of assembly positions, for each type of car which is to be manufactured. For example, if different types of coal cars are to be manufactured, it would be expensive to provide a line to manufacture each type of coal car.
It would be desirable to provide a line for the assembly of coal cars in which different types of coal car bottoms could be utilized and assembled in a single line with common stub sills, sides and end structures. Such a line would enable the production of stock sub-assemblies of stub sills, sides, end structures and hopper bottoms. The customer may then select the type of coal carrying bottom he desires. Such an assembly procedure offers considerable economic benefits over the use of a separate line for each type of coal car.
In U.S. Pat. No. 4,206,709, a covered hopper car is disclosed which is convertible from a liquid carrying hopper car to a conventional hopper car adapted to carry particulate solid lading. However, this covered hopper car patent gives no teaching of the sub-assembly of stub sills, sides and ends in a single line, and the liquid carrying bottom is replaced with a pneumatic hopper outlet.